Method for depositing silicon oxide film having improved quality by peald using bis(diethylamino)silane

ABSTRACT

In a method of depositing a silicon oxide film using bis(diethylamino)silane (BDEAS) on a substrate in a reaction space by plasma-enhanced atomic layer deposition (PEALD), each repeating deposition cycle of PEALD includes steps of: (i) adsorbing BDEAS on the substrate placed on a susceptor having a temperature of higher than 400° C. in an atmosphere substantially suppressing thermal decomposition of BDEAS in the reaction space; and (ii) exposing the substrate on which BDEAS is adsorbed to an oxygen plasma in the atmosphere in the reaction space, thereby depositing a monolayer or sublayer of silicon oxide.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/891,160, filed on Aug. 23, 2019, in the United States Patent andTrademark Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention generally relates to a method for depositing asilicon oxide film having improved quality (e.g., excellent chemicalresistance such as low wet etching rate, particularly at sidewalls andbottom of a trench) by plasma-enhanced atomic layer deposition (PEALD)using bis(diethylamino)silane (BDEAS).

Description of the Related Art

As a method of depositing a silicon oxide film by PEALD, a depositionmethod using BDEAS and oxygen plasma is known. However, when depositinga silicon oxide film in a trench formed in a substrate using theconventional method, film quality (chemical resistance such as low dryor wet etching rate, leakage current, shrinkage, in-plane uniformity,etc.) at sidewalls and bottom of the trench tends to be insufficient orunsatisfactory as compared with film quality on a top surface of thesubstrate. In general, by increasing RF power and/or duration of an RFpower pulse, film quality is expected to be improved. However, when thetrench has a high aspect ratio (e.g., 3 or higher, particularly 10 orhigher), sufficient improvement of film quality has not been achieved,particularly at film quality at sidewalls and bottom of the trench, dueto directionality or the anisotropic nature of plasma (e.g., ionbombardment by direct plasma composed of ions).

In view of the conventional technology, an embodiment of the presentinvention provides a method for depositing a silicon oxide film havingimproved quality by PEALD using BDEAS.

Any discussion of problems and solutions involved in the related art hasbeen included in this disclosure solely for the purposes of providing acontext for the present invention, and should not be taken as anadmission that any or all of the discussion were known at the time theinvention was made.

SUMMARY OF THE INVENTION

As discussed above, as process parameters, increasing RF power and/orduration of an RF power pulse may not be sufficient or effective toimprove film quality at sidewalls and bottom of a trench in depositing asilicon oxide film by PEALD using BDEAS due to the anisotropic nature ofplasma. Thus, as a process parameter, increasing a depositiontemperature can be considered to be a good candidate. However, a skilledartisan in the art is likely to consider that BDEAS starts thermaldecomposition at a temperature higher than 400° C., and thus, in orderto obtain a high-quality silicon oxide film using BDEAS, the processtemperature in PEALD should preferably be 400° C. or lower. For example,U.S. Pat. No. 8,227,032 states that high quality films, with very lowcarbon and hydrogen contents, are preferably deposited between 200 and400° C. If BDEAS is thermally decomposed, amines, oxides of carbon,oxides of nitrogen, and oxides of silicon are produced as thermaldecomposition products, resulting in deposition of a silicon oxide filmhaving relatively high contents of carbon, nitrogen, and hydrogen.Further, for example, WO2016/954531 states that the wafer surface isheated to a temperature in the range of about 450° C. to about 650° C.,so that the absorbed silicon precursor thermally decomposes on the wafersurface to form a monolayer or sub-monolayer silicon film. As discussedabove, a skilled artisan is fairly likely to expect BDEAS also to bethermally decomposed at a temperature higher than 400° C. It should benoted that, unlike typical PEALD where an adsorbed silicon precursorcontaining carbon/nitrogen reacts with an oxygen plasma and forms asilicon oxide film by displacement reaction displacing carbon/nitrogenby oxygen, in WO2016/954531, first, the absorbed silicon precursorthermally decomposes on the wafer surface to form a monolayer orsub-monolayer silicon film, and then is exposed to a source of oxygen,thereby oxidizing the silicon film to form a SiO₂ film.

Contrary to the skilled artisan's expectation, the present inventorshave discovered that BDEAS is stable and is not significantly decomposedat a temperature of higher than 400° C. but no higher than 650° C., andby using such a high temperature as a deposition temperature by PEALD,film quality of a deposited silicon oxide film can be significantlyimproved, particularly, at sidewalls and bottom of a trench. In someembodiments, in a method of depositing a silicon oxide film using BDEASon a substrate in a reaction space by PEALD, each repeating depositioncycle of PEALD comprises steps of: (i) adsorbing BDEAS on the substrateplaced on a susceptor having a temperature of higher than 400° C. in anatmosphere substantially suppressing thermal decomposition of BDEAS inthe reaction space; and (ii) exposing the substrate on which BDEAS isadsorbed to an oxygen plasma in the atmosphere in the reaction space,thereby depositing a monolayer of silicon oxide.

In some embodiments, the temperature of the susceptor is lower than 650°C. In some embodiments, the atmosphere has a pressure of 1,000 Pa orless and an oxygen concentration of 5% to 70%. Further, in someembodiments, the atmosphere has a pressure of 400 Pa or less. Still insome embodiments, the atmosphere has an oxygen concentration of 30% to60%.

For purposes of summarizing aspects of the invention and the advantagesachieved over the related art, certain objects and advantages of theinvention are described in this disclosure. Of course, it is to beunderstood that not necessarily all such objects or advantages may beachieved in accordance with any particular embodiment of the invention.Thus, for example, those skilled in the art will recognize that theinvention may be embodied or carried out in a manner that achieves oroptimizes one advantage or group of advantages as taught herein withoutnecessarily achieving other objects or advantages as may be taught orsuggested herein.

Further aspects, features and advantages of this invention will becomeapparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will now be described withreference to the drawings of preferred embodiments which are intended toillustrate and not to limit the invention. The drawings are greatlysimplified for illustrative purposes and are not necessarily to scale.

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1A is a schematic representation of a PEALD (plasma-enhanced atomiclayer deposition) apparatus for depositing a silicon oxide film, usablein an embodiment of the present invention.

FIG. 1B illustrates a schematic representation of a precursor supplysystem using a flow-pass system (FPS) usable in an embodiment of thepresent invention.

FIG. 2 shows a schematic process sequence of PEALD in one according toan embodiment of the present invention wherein a cell in gray representsan ON state whereas a cell in white represents an OFF state, and thewidth of each column does not represent duration of each process.

FIG. 3 shows a graph indicating the schematic relationship between filmthickness and susceptor temperature in Reference Example 1.

FIG. 4 is a chart showing STEM photographs of cross-sectional views oftrenches subjected to deposition of silicon oxide films at differenttemperatures (“As depo”), followed by wet etching (“After DHF dip”).

FIG. 5 is a chart showing STEM photographs of cross-sectional views oftrenches subjected to deposition of silicon oxide films at differentpressures, different oxygen concentration, and different durations ofpurging (“As depo”), followed by wet etching (“After DHF dip”).

FIG. 6 is a chart showing the deposition conditions used in depositionshown in FIG. 4 , and film properties of resultant silicon oxide films,including color versions of images of thin-film thickness profilemeasurement by 2D color map analysis of the films.

FIG. 7 is a schematic graph showing the relationship between wet etchingrate and plasma bombardment on a surface according to an embodiment ofthe present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

In this disclosure, “gas” may include vaporized solid and/or liquid andmay be constituted by a single gas or a mixture of gases, depending onthe context. Likewise, an article “a” or “an” refers to a species or agenus including multiple species, depending on the context. In thisdisclosure, a process gas introduced to a reaction chamber through ashowerhead may be comprised of, consist essentially of, or consist of anaminosilane precursor and an additive gas. The precursor may containonly bis(diethylamino)silane (BDEAS) or contain BDEAS as a primaryprecursor and one or more secondary precursor(s) which is/are eitheraminosilane or non-aminosilane to the extent not interfering with plasmaoxidation of BDEAS to form silicon oxide. The additive gas may include aplasma-generating gas for exciting the precursor to deposit siliconoxide when RF power is applied to the additive gas. The additive gas maycontain a reactant gas for oxidizing the precursor and may furthercontain an inert gas which may be fed to a reaction chamber as a carriergas and/or a dilution gas to the extent not interfering with plasmaoxidation forming silicon oxide. The precursor and the additive gas canbe introduced as a mixed gas or separately to a reaction space. Theprecursor can be introduced with a carrier gas such as a rare gas. A gasother than the process gas, i.e., a gas introduced without passingthrough the showerhead, may be used for, e.g., sealing the reactionspace, which includes a seal gas such as a rare gas. In someembodiments, the term “precursor” refers generally to a compound thatparticipates in the chemical reaction that produces another compound,and particularly to a compound that constitutes a film matrix or a mainskeleton of a film, whereas the term “reactant” refers to a compound,other than precursors, that activates a precursor, modifies a precursor,or catalyzes a reaction of a precursor, wherein the reactant may providean element (such as O) to a film matrix and become a part of the filmmatrix, when RF power is applied. The term “inert gas” refers to aplasma-generating gas that excites a precursor when RF power is applied,but unlike a reactant, it does not become a part of a film matrix.

In some embodiments, “a monolayer” refers to a layer one molecule thick,and “a sublayer” refers to a subunit of layer which is not necessarily amonolayer but is a layer deposited in one cycle of ALD as a subunit partof a final film. In some embodiments, “film” refers to a layercontinuously extending in a direction perpendicular to a thicknessdirection substantially without pinholes to cover an entire target orconcerned surface, or simply a layer covering a target or concernedsurface. In some embodiments, “layer” refers to a structure having acertain thickness formed on a surface or a synonym of film or a non-filmstructure. A film or layer may be constituted by a discrete single filmor layer having certain characteristics or multiple films or layers, anda boundary between adjacent films or layers may or may not be clear andmay be established based on physical, chemical, and/or any othercharacteristics, formation processes or sequence, and/or functions orpurposes of the adjacent films or layers. Further, in this disclosure,any two numbers of a variable can constitute a workable range of thevariable as the workable range can be determined based on routine work,and any ranges indicated may include or exclude the endpoints.Additionally, any values of variables indicated (regardless of whetherthey are indicated with “about” or not) may refer to precise values orapproximate values and include equivalents, and may refer to average,median, representative, majority, etc. in some embodiments. Further, inthis disclosure, the terms “constituted by” and “having” referindependently to “typically or broadly comprising”, “comprising”,“consisting essentially of”, or “consisting of” in some embodiments. Inthis disclosure, any defined meanings do not necessarily excludeordinary and customary meanings in some embodiments.

In this disclosure, “continuously” refers to without breaking a vacuum,without interruption as a timeline, without any material interveningstep, without changing treatment conditions, immediately thereafter, asa next step, or without an intervening discrete physical or chemicalstructure between two structures other than the two structures in someembodiments.

In this disclosure, a “step” or “recess” refers to any structure havinga top surface, a sidewall, and a bottom surface formed on a substrate,which may continuously be arranged in series in a height direction ormay be a single step, and which may constitute a trench, a via hole, orother recesses. Further, in this disclosure, a trench is any recesspattern including a hole/via and which has, in some embodiments, a widthof 10 to 50 nm (typically 15 to 30 nm) (wherein when the trench has alength substantially the same as the width, it is referred to as ahole/via, and a diameter thereof is 10 to 50 nm), a depth of 30 to 200nm (typically 50 to 150 nm), and an aspect ratio of 3 to 20 (typically 3to 10).

In this disclosure, a SiO film includes not only SiO films, but alsoSiOC films, SiON films, SiOCN films, or the like, depending on theprocess recipe, wherein the film names are abbreviations indicatingmerely the film types (indicated simply by primary constituent elements)in a non-stoichiometric manner unless described otherwise.

FIG. 2 shows a schematic process sequence of PEALD in one according toan embodiment of the present invention wherein a cell in gray representsan ON state whereas a cell in white represents an OFF state, and thewidth of each column does not represent duration of each process. Afirst step (“Feed”) comprises feeding BDEAS to a reaction space in apulse and adsorbing BDEAS on a substrate placed on a susceptor having atemperature of higher than 400° C. (preferably higher than 500° C. butnot higher than 650° C.) in an atmosphere substantially suppressingthermal decomposition of BDEAS in the reaction space. In general, thehigher the temperature, the more the improvement of film quality of aresultant silicon oxide film, particularly at sidewalls and bottom ofthe trench, can be expected as long as thermal decomposition of BDEAScan sufficiently or substantially be suppressed in the atmosphere.Preferably, the atmosphere has a pressure of 1,000 Pa or less (morepreferably 400 Pa or less, e.g., 333 Pa to 400 Pa) and an oxygenconcentration of 5% to 70% (more preferably an oxygen concentration of30% to 60%) so that even when the deposition temperature is high,thermal decomposition of BDEAS can be suppressed. In some embodiments,oxygen as an oxidizer is fed to the reaction space at a flow rate of 400sccm to 5600 sccm (preferably 1600 sccm to 4000 sccm) with one or moreinert gas (e.g., rare gas such as Ar and/or He) fed at a flow rate of400 sccm to 5600 sccm (preferably 2000 sccm to 4400 sccm). As anoxidizer, nitrogen dioxide can also be used. In this embodiment, theoxidizer is fed continuously throughout the deposition cycle. In the“Feed” step, BDEAS is fed using a flow of carrier gas which is an inertgas such as rare gas (e.g. Ar and/or He) fed at a flow rate of 2000sccm. Since ALD is a self-limiting adsorption reaction process, theamount of deposited precursor molecules is determined by the number ofreactive surface sites and is independent of the precursor exposureafter saturation, and a supply of the precursor is such that thereactive surface sites are saturated thereby per cycle (“chemisorption”refers to chemical saturation adsorption). In this embodiment, thecarrier gas is fed continuously throughout the deposition cycle.

The continuous flow of the carrier gas can be accomplished using aflow-pass system (FPS) wherein a carrier gas line is provided with adetour line having a precursor reservoir (bottle), and the main line andthe detour line are switched, wherein when only a carrier gas isintended to be fed to a reaction chamber, the detour line is closed,whereas when both the carrier gas and a precursor gas are intended to befed to the reaction chamber, the main line is closed and the carrier gasflows through the detour line and flows out from the bottle togetherwith the precursor gas. In this way, the carrier gas can continuouslyflow into the reaction chamber and can carry the precursor gas in pulsesby switching between the main line and the detour line. FIG. 1Billustrates a precursor supply system using a flow-pass system (FPS)according to an embodiment of the present invention (black valvesindicate that the valves are closed). As shown in (a) in FIG. 1B, whenfeeding a precursor to a reaction chamber (not shown), first, a carriergas such as Ar (or He) flows through a gas line with valves b and c, andthen enters a bottle (reservoir) 20. The carrier gas flows out from thebottle 20 while carrying a precursor gas in an amount corresponding to avapor pressure inside the bottle 20 and flows through a gas line withvalves f and e, and is then fed to the reaction chamber together withthe precursor. In the above, valves a and d are closed. When feedingonly the carrier gas (noble gas) to the reaction chamber, as shown in(b) in FIG. 1B, the carrier gas flows through the gas line with thevalve a while bypassing the bottle 20. In the above, valves b, c, d, e,and f are closed.

In some embodiments, the duration of “Feed” is 0.1 seconds to 3.0seconds (preferably 0.2 seconds to 0.5 seconds).

Next, in the second step (“Purge-1”), the reaction space is purged so asto remove excess BDEAS and non-adsorbed BDEAS from the surface of thesubstrate. The purging can be accomplished simply by continuous flows ofoxidizer and carrier gas which function as a purging gas, although aseparate purging gas can be used. In some embodiments, the duration ofpurge is 0.2 seconds to 2.0 seconds (preferably 0.3 seconds to 1.0seconds). In some embodiments, in PEALD, by shortening a duration ofpurge (e.g., to a range of 0.1 seconds to 0.5 seconds), somenon-adsorbed BDEAS may remain on the top surface and in the trench, andthis may result in lowering film quality on the top surface and at thebottom of the trench, while improving film quality on the sidewalls to acertain degree. This may be because a shorter duration of purge leavesmore BDEAS in the trench which may stay in the trench like cloud whichmay partially block plasma from reaching the bottom, while more plasmaenergy reaches the sidewalls.

Next, in the third step (“RF Pulse”), BDEAS adsorbed on the substratesurface is exposed to an oxygen plasma, thereby depositing a monolayeror sublayer of silicon oxide on the substrate. In some embodiments, theperiod of RF power application (the period of being exposed to a plasma)is in a range of 0.2 seconds to 2.0 seconds (preferably 0.2 seconds to1.2 seconds). The plasma exposure time can also be adjusted by changingthe distance between upper and lower electrodes when conductivelycoupled parallel electrodes are used wherein by increasing the distance,the retention time in which the precursor is retained in the reactionspace between the upper and lower electrodes can be prolonged when theflow rate of precursor entering into the reaction space is constant. Insome embodiments, the distance (mm) between the upper and lowerelectrodes is 7.5 mm to 13 mm (preferably 7.5 mm to 10 mm). In someembodiments, RF power (W) (e.g., 13.56 MHz) for deposition is 50 W to1000 W (preferably 200 W to 500 W) as measured for a 300-mm wafer whichcan be converted to units of W/cm² for different sizes of wafers.

After the third step, in the fourth step (“Purge-2”), the reaction spaceis purged so as to remove unreacted BDEAS and reaction by-products fromthe surface of the substrate. The purging can be accomplished simply bycontinuous flows of oxidizer and carrier gas which function as a purginggas, although a separate purging gas can be used. In some embodiments,the duration of purge is 0.1 seconds to 1.0 seconds (preferably 0.1seconds to 0.3 seconds).

The process cycle can be performed using any suitable apparatusincluding an apparatus illustrated in FIG. 1A, for example. FIG. 1A is aschematic view of a PEALD apparatus, desirably in conjunction withcontrols programmed to conduct the sequences described below, usable insome embodiments of the present invention. In this figure, by providinga pair of electrically conductive flat-plate electrodes 4, 2 in paralleland facing each other in the interior 11 (reaction zone) of a reactionchamber 3, applying HRF power (13.56 MHz or 27 MHz) 25 to one side, andelectrically grounding the other side 12, a plasma is excited betweenthe electrodes. A temperature regulator is provided in a lower stage 2(the lower electrode), and a temperature of a substrate 1 placed thereonis kept constant at a given temperature. The upper electrode 4 serves asa shower plate as well, and reactant gas and/or dilution gas, if any,and precursor gas are introduced into the reaction chamber 3 through agas line 21 and a gas line 22, respectively, and through the showerplate 4. Additionally, in the reaction chamber 3, a circular duct 13with an exhaust line 7 is provided, through which gas in the interior 11of the reaction chamber 3 is exhausted. Additionally, a transfer chamber5 disposed below the reaction chamber 3 is provided with a seal gas line24 to introduce seal gas into the interior 11 of the reaction chamber 3via the interior 16 (transfer zone) of the transfer chamber 5 wherein aseparation plate 14 for separating the reaction zone and the transferzone is provided (a gate valve through which a wafer is transferred intoor from the transfer chamber 5 is omitted from this figure). Thetransfer chamber is also provided with an exhaust line 6. In someembodiments, the deposition of multi-element film and surface treatmentare performed in the same reaction space, so that all the steps cancontinuously be conducted without exposing the substrate to air or otheroxygen-containing atmosphere.

In some embodiments, in the apparatus depicted in FIG. 1A, the system ofswitching flow of an inactive gas and flow of a precursor gasillustrated in FIG. 1B (described earlier) can be used to introduce theprecursor gas in pulses without substantially fluctuating pressure ofthe reaction chamber.

A skilled artisan will appreciate that the apparatus includes one ormore controller(s) (not shown) programmed or otherwise configured tocause the deposition and reactor cleaning processes described elsewhereherein to be conducted. The controller(s) are communicated with thevarious power sources, heating systems, pumps, robotics and gas flowcontrollers, or valves of the reactor, as will be appreciated by theskilled artisan.

In some embodiments, a dual chamber reactor (two sections orcompartments for processing wafers disposed close to each other) can beused, wherein a reactant gas and a noble gas can be supplied through ashared line whereas a precursor gas is supplied through unshared lines.

The film having filling capability can be applied to varioussemiconductor devices including, but not limited to, cell isolation in3D cross point memory devices, self-aligned Via, dummy gate (replacementof current poly Si), reverse tone patterning, PC RAM isolation, cut hardmask, and DRAM storage node contact (SNC) isolation.

EXAMPLES

In the following examples where conditions and/or structures are notspecified, the skilled artisan in the art can readily provide suchconditions and/or structures, in view of the present disclosure, as amatter of routine experimentation. A skilled artisan will appreciatethat the apparatus used in the examples included one or morecontroller(s) (not shown) programmed or otherwise configured to causethe deposition and reactor cleaning processes described elsewhere hereinto be conducted. The controller(s) were communicated with the variouspower sources, heating systems, pumps, robotics and gas flow controllersor valves of the reactor, as will be appreciated by the skilled artisan.

Reference Example 1 (Thermal Stability of BDEAS)

In Reference Example 1, in order to examine thermal stability of BDEAS,a Si substrate on which a native or natural oxide film having athickness of 1.20 nm was formed was placed in the apparatus illustratedin FIG. 1A with a gas supply system (FPS) illustrated in FIG. 1B. Theatmosphere of the reaction chamber was controlled by feeding theretoBDEAS at 2000 sccm and oxygen at 2000 sccm under a pressure of 400 Pawithout applying RF power to the reaction chamber, wherein a susceptortemperature was set in a range of 400° C. to 650° C. 800 seconds afterthe susceptor temperature reached the set temperature, the thickness ofthe film was measured at each set temperature. As a comparativereference example, the thickness of film was measured at each settemperature in the same manner as in Reference Example 1 except that noBDEAS was fed to the reaction chamber.

FIG. 3 shows a graph indicating the schematic relationship between filmthickness and susceptor temperature. As shown in FIG. 3 , the thicknessof the film with the BDEAS feed (“w/Feed”) and the thickness of the filmwithout the BDEAS feed (“w/o Feed”) were substantially the same in theentire temperature range. It should be noted that the thickness of thefilm appeared to increase as the temperature became higher even when noBDEAS was fed, and this is because the substrate itself (with theunderlying natural oxide film) was further oxidized by oxygen,increasing the apparent thickness. Further, the film thickness wasslightly greater when BDEAS was fed than when no BDEAS was fed attemperatures of 550° C., 600° C., and 650° C. This is because BDEAS wasadsorbed on the substrate surface by heat. If BDEAS had been thermallydecomposed at the set temperature, decomposed components (such as amine,oxide of carbon, oxide of nitrogen, and oxide of silicon) would havebeen continuously accumulated on the substrate surface, significantlyincreasing the film thickness particularly at higher temperatures. Thus,the result shown in FIG. 3 confirms that BDEAS is not thermallydecomposed in a temperature range of 400° C. to 650° C.

Example 1 (Improvement of Film Quality at High Deposition Temperatures)

A silicon oxide film was deposited on a Si substrate (having a diameterof 300 mm and a thickness of 0.7 mm) having trenches with an opening ofapproximately 30 nm, which had a depth of approximately 90 nm (an aspectratio was approximately 3), by PEALD process in order to determine filmquality of the film, under the conditions shown in Table 1 below(varying the deposition temperature) in the process sequence illustratedin FIG. 2 using the apparatus illustrated in FIG. 1A and a gas supplysystem (FPS) illustrated in FIG. 1B. After deposition of silicon oxidefilm was complete, a cross-sectional view of each substrate with thetrenches was photographed using STEM.

TABLE 1 (numbers are approximate) Temp. setting SUS temp (° C.). SeeFIG. 4 Depo Pressure (Pa) 400 Electrode Gap (mm) 7.5 Feed time (s) 0.2Purge-1 (s) 0.3 RF time (s) 1 Purge-2 (s) 0.1 RF power (W) 500 PrecursorBDEAS Carrier Ar Carrier flow (slm) 2.0 Dilution Ar (slm) 2.0 Seal He(slm) 0.2 O2 (slm) 4.0 Number of cycles 500

After completion of deposition of each silicon oxide film (having anaverage film thickness of 25 nm on the top surface), the substrate wassubjected to wet etching (by dipping the substrate in a solution of dHFhaving a concentration of 1% for 30 seconds at 22° C.). Further, afterwet etching, a cross-sectional view of each substrate with the trencheswas photographed using STEM.

FIG. 4 is a chart showing STEM photographs of cross-sectional views oftrenches subjected to deposition of silicon oxide films at differenttemperatures (“As depo”), followed by wet etching (“After DHF dip”). InFIG. 4 , “Side/Top [%]” refers to a ratio [%] of thickness of thesidewall portion when deposited to that of the top portion, and “WERR[TOX ratio]” refers to wet etching rate of each portion relative to thatof standard thermal oxide film. As shown in FIG. 4 , when the depositiontemperature was 400° C. or higher, particularly higher than 500° C.(more preferably 550° C. or higher), the film quality of the sidewallportion was improved.

Example 2 (Improvement of Film Quality with Other Parameters)

A silicon oxide film was deposited on a Si substrate in the same manneras in Example 1 except the conditions shown in Table 2 below.

TABLE 2 (numbers are approximate) Temp. UHT-6 UHT-7 UHT-8 UHT-9 UHT-10UHT-11 setting SUS temp (° C.). 650 Depo Pressure (Pa) 400 400 1000 3000400 400 Purge-1 (s) 0.3 2 2 2 0.3 0.3 Carrier Ar (slm) 2.0 2.0 2.0 2.02.0 0.4 Dilution Ar (slm) 2.0 2.0 2.0 2.0 5.6 2.0 O2 (slm) 4.0 4.0 4.04.0 0.4 5.6 O2/(O2 + Ar) (%) 50 50 50 50 5 70

After completion of deposition of each silicon oxide film, the substratewas subjected to wet etching in the same manner as in Example 1.Further, after wet etching, a cross-sectional view of each substratewith the trenches was photographed using STEM. It should be noted thatwhen the deposition pressure was 3,000 Pa in UHT-9, film depositionbecame highly abnormal and thus, wet etch evaluation of this sample wasnot conducted.

FIG. 5 is a chart showing STEM photographs of cross-sectional views ofthe trenches subjected to deposition of the silicon oxide films atdifferent pressures, different oxygen concentration, and differentdurations of purging (“As depo”), followed by wet-etching (“After DHFdip”). In FIG. 5 , “Side/Top [%]” and “WERR [TOX ratio]” denote the samemeanings as in FIG. 4 . As shown in FIG. 5 , at a high depositiontemperature (650° C.), when the deposition pressure was 400 Pa in UHT-7,as compared with in UHT-8 (1,000 Pa), the film quality of the sidewallportion was improved. However, the film quality of the top portion wasnot improved at a pressure of 400 Pa in UHT-7, as compared with in UHT-8(1,000 Pa), and the film quality of the bottom portion was worsened at apressure of 400 Pa in UHT-7, as compared with in UHT-8 (1,000 Pa). Thismay be because plasma bombardment received by a surface of each portionwould be in the order of Top (400 Pa)>Top (1000 Pa)>Bottom (400Pa)>Bottom (1000 Pa)>Side (400 Pa)>Side (1000 Pa), and there would beoptimal plasma bombardment for improving film quality around at Bottom(1000 Pa), and when plasma bombardment is higher or lower than theoptimal plasma bombardment, film quality would be less improved asschematically illustrated in FIG. 7 . A plasma is a partially ionizedgas with high free electron content (about 50%), and when a plasma isexcited by applying AC voltage between parallel electrodes, ions areaccelerated by a self dc bias (VDc) developed between plasma sheath andthe lower electrode and bombard a film on a substrate placed on thelower electrode in a direction perpendicular to the film (the ionincident direction). Based on this non-limiting theory, a skilledartisan would be able to adjust film quality of each portion as desiredby manipulating the deposition pressure (by doing this, film quality ofthe bottom portion and that of the sidewall portion (and further that ofthe top portion) can be adjusted at substantially the same degree). Thebombardment of a plasma can be represented by plasma density (quantityof plasma active species) or kinetic energy of ions, and plasma densitycan be evaluated as disclosed in United States Patent Publication No.2017/0250068, the disclosure of which is herein incorporated byreference in its entirety.

Also as shown in FIG. 5 , at a high deposition temperature (650° C.),when a concentration of oxygen in the oxidizer gas (oxygen plus argon inthis embodiment) was 50% in UHT-6, as compared with in UHT-10 (5%) andUHT-11 (70%), the film quality of the sidewall portion was improved.However, the film quality of the top portion was worsened at aconcentration of oxygen of 50% in UHT-6, as compared with in UHT-10 (5%)and UHT-11 (70%). This may be because not only an oxygen plasma but alsoan argon plasma contributes to film quality of the sidewall portion, andwhen a ratio of an oxygen concentration and an argon concentration isapproximately equal (e.g., ±10%, i.e., 40% to 60%), film quality of thesidewall portion can significantly be improved. Based on thisnon-limiting theory, a skilled artisan would be able to adjust filmquality of each portion as desired by manipulating the oxygenconcentration.

Further, as shown in FIG. 5 , at a high deposition temperature (650°C.), when a duration of purge was 0.3 seconds in UHT-6, as compared within UHT-7 (2.0 seconds), the film quality of the sidewall portion wasimproved. However, the film quality of the top portion and that of thebottom portion were worsened at a duration of purge of 0.3 seconds inUHT-6, as compared with in UHT-7 (2.0 seconds). This may be because somenon-adsorbed BDEAS may remain on the top surface and in the trench in aduration of purge of 0.3 seconds, and this may result in lowering filmquality of the top portion and that of the bottom portion, whileimproving film quality of the sidewall portion to a certain degree. Thismay be because a shorter duration of purge leaves more BDEAS in thetrench which may stay in the trench like cloud which may partially blockplasma from reaching the bottom, while more plasma energy reaches thesidewalls. Based on this non-limiting theory, a skilled artisan would beable to adjust film quality of each portion as desired by manipulatingthe oxygen concentration.

Example 3 (Improvement of Film Quality—Blanket Deposition)

A silicon oxide film was deposited on a Si substrate without trenches inthe same manner as in Example 1 except this was blanket deposition (notpattern deposition).

After completion of deposition of each silicon oxide film, the substratewas subjected to wet etching in the same manner as in Example 1.Further, after wet etching, film properties of each silicon oxide filmwere evaluated in terms of average thickness, in-plane thicknessuniformity, and wet etching rate.

FIG. 6 is a chart showing the deposition conditions used in depositionshown in FIG. 4 , and film properties of the resultant silicon oxidefilms, including color versions of images of thin-film thickness profilemeasurement by 2D color map analysis of the films. In FIG. 6 , “1^(st)WERR/TOX” refers to wet etching rate of each film relative to that ofstandard thermal oxide film, measured for the first one minute of wetetching, while “2nd WERR/TOX” refers to wet etching rate of each filmrelative to that of standard thermal oxide film, measured for the secondone minute of wet etching. As shown in FIG. 6 , at a high depositiontemperature (650° C.), when a deposition pressure was 3,000 Pa in UHT-9,as compared with in UHT-6, -7, and -8 (400 Pa), the film deposition washighly abnormal, and no film quality was evaluated. Further, when adeposition pressure was 1,000 Pa in UHT-8, as compared with in UHT-6 and-7 (400 Pa), film quality was worsened, although it was within normaldeposition. Further, as shown in FIG. 6 , the oxygen concentration of 5%to 70% was a workable range for providing adequate film quality.

It will be understood by those of skill in the art that numerous andvarious modifications can be made without departing from the spirit ofthe present invention. Therefore, it should be clearly understood thatthe forms of the present invention are illustrative only and are notintended to limit the scope of the present invention.

We claim:
 1. A method of depositing a silicon oxide film usingbis(diethylamino)silane (BDEAS) on a substrate in a reaction space byplasma-enhanced atomic layer deposition (PEALD), each repeatingdeposition cycle of PEALD comprising steps of: (i) adsorbing BDEAS onthe substrate placed on a susceptor having a temperature of higher than500° C.; (ii) purging the reaction space; (iii) exposing the substrateon which BDEAS is adsorbed to an oxidizer gas in an atmosphere in thereaction space, and applying an RF power, thereby depositing a monolayeror sublayer of silicon oxide, wherein the atmosphere has an oxygenconcentration of 5% to 70% by volume in a carrier gas; and (iv) purgingthe reaction space; wherein the oxidizer gas is fed to the reactionspace continuously throughout the deposition cycle, and wherein apressure within the reaction space is less than 1000 Pa.
 2. The methodaccording to claim 1, wherein the temperature of the susceptor is nothigher than 650° C.
 3. The method according to claim 1, wherein theatmosphere has a pressure of 400 Pa or less.
 4. The method according toclaim 1, wherein the atmosphere has an oxygen concentration of 30% to60% by volume.
 5. The method according to claim 1, wherein one or moreof the (ii) purging the reaction space and the (iv) purging is conductedfor less than 2.0 seconds.
 6. The method according to claim 1, whereinthe oxidizer gas comprises nitrogen dioxide.
 7. The method according toclaim 1, wherein in step (ii), oxidizer gas is fed to the reaction spaceat a flow rate of between 1600 and 4000 sccm, and an inert gas is fed tothe reaction space at a flow rate of between 2000 and 4400 sccm.
 8. Themethod according to claim 1, wherein the substrate comprises a trench,and wherein the silicon oxide film is deposited on the sidewalls and thebottom surface of the trench.
 9. The method of claim 1, wherein thecarrier gas is fed to the reaction space continuously throughout thedeposition cycle, and wherein in step (i), the BDEAS is provided to thereaction space in a pulse by flowing the carrier gas through a bottlecarrying the BDEAS.
 10. The method of claim 1, wherein the oxygenconcentration is 50% to 70% by volume.
 11. The method of claim 1,wherein the oxidizer gas consists essentially of oxygen and the carriergas.
 12. The method of claim 11, wherein the carrier gas is a noble gas.13. The method according to claim 1, wherein the substrate has apatterned step on which BDEAS is adsorbed in step (i).
 14. The methodaccording to claim 13, wherein the patterned step is a trench having anaspect ratio of 3 or higher.